Already in 1930's it was found out by Langmuir and Blodgett that fatty acids having about 16 to 22 carbon atoms form a monomolecular film on the surface of water and such a film can be built up on a substrate, but it is only within recent years that its technical application began to be investigated.
The outline of the investigation hitherto made has been reviewed in "Kotai Butsuri" (Physics of Solids) 17 (12) 45 (1982), Thin Solid Film 68 No. 1 (1980), ibid, 99 No. 1, 2, 3 (1983), Insoluble monolayers at liquid-gas interface (G. L. Gains, Interscience Publishers, New York, 1966), etc., but the conventional Langmuir-Blodgett films (hereinafter referred to as "LB film") of straight chain saturated carboxylic acids are defective in the points of heat resistance and mechanical strength, and so there is a problem that they can find no practical application as they are.
In order to improve these defects investigations were made on polymerized films of unsaturated fatty acids such as .omega.-tricosenic acid, .omega.-heptadecenic acid, or .alpha.-octadecylacrylic acid; unsaturated esters of fatty acids such as vinyl stearate, octadecyl acrylate; and besides these, diacetylene derivatives, etc., but they can be said to be neither sufficiently heat-resistant nor electrically excellent. As for polymers, it is known that some of the high polymers having hydrophilic groups such as polyacids, polyalcohols, ethyl acrylate, polypeptides, etc. are possessed of a film-forming property, but any sort of modified high polymer suitable for LB materials has not as yet been investigated, and there are no excellent material for the LB film worthy of the name.
On the other hand, as a heat-resistant film there may be mentioned polyimide, but the thickness of the film of this material obtained according to the spin coating process is not less than 1000 .ANG., and usually not less than 1 micron, so that it is very difficult to produce heat-resistant thin film of a thickness not more than 1000 .ANG. and free from pin holes.